Several types of rolls are needed in paper making industry and oftentimes heavy loads are applied on the rolls. The load on the elements changes for several reasons and pulsates because of the rotation of the element. This causes displacements between the roll and the elements carrying the roll, and in some cases there is even need to move the axle of the roll in relation to the housing of the bearing element or an other frame element carrying the roll. If roller or ball bearings are used, the the sealing requirements are not as high as those of the seals of the slide bearings since the oil flow and pressure is less than in roller and ball bearings. In pressurized slide bearings, pressurized oil is pumped between the sliding surfaces, and the oil flows are notable. The pressure of the oil is normally low outside the bearing, but may in some cases exceed the normally used oil pressure in a lubrication oil circulation.
At present, most dynamic seals available allow some movement in radial or axial direction, but few designs allow combination of both movements at the same time, and the movements are usually limited to a few millimeters. However, in highly loaded rolls, the axles of the rolls bend during operation, and both radial and axial displacement occurs due to the angular displacement of the ends of the roll. Radial and axial displacement may occur also for different operational reasons, for example in some novel designs the position of the slide bearing within the bearing box may be changed to control a nip or gap formed by two adjacent rolls. When the position of the axle of the roll changes, its position in the bearing box changes, thereby causing the clearance between the axle and its seat in the bearing box to change. Presently available seals cannot accommodate such changes if displacements are large.
One known sealing structure for sealing the ends of rolls having a rotating shell mounted on slide bearings comprises a slide ring seal that is pressed against the end wall of the end plate of the roll shell by a spring loaded piston. The sealing structure also comprises a ring-formed conventional lip seal mounted on the end wall of the roll shell, and a backing ring. The backing ring forms a sliding surface for the rotating lip seal, and the ring is attached to the sliding ring seal, whereby the piston of the ring seal presses the backing ring against the lip seal and contact between the lip seal and the backing ring is maintained. The sealing contact is maintained during the radial movement between the roll shell and the roll axle by a wide sliding surface of the backing ring. This arrangement provides a reasonably wide radial movement area over which a good seal is maintained. However, the axial movement area is only a few millimeters and is determined by the movement range of the piston loaded ring seal. The ring seal has to be very precisely set against its sliding surface on the end plate of the roll shell. Therefore, the movement of the ring seal is limited. Especially angular movements of the roll axle are problematic to the ring seal and the lip seal that are attached together in the above described manner, since if the angle of the end plate changes in relation to the ring seal the backing ring attached to the ring seal may detach from the lip seal. Angular displacement may even cause the ring seal to loose its sealing contact.
As described above presently available seal constructions do not allow simultaneous relative movement in an axial and radial direction of two rotating components. However, in modern paper making machines such movents do occur in several elements, for example in rolls of film transfer coaters.